In very high throughput satellite systems with multibeam coverage and with frequency reuse between beams, the allocation of the resources in terms of frequency and radio power is generally fixed by design of the satellite's payload. Typically, in a very high throughput satellite system operating in the Ka band (20/30 GHz), to each beam of the coverage is allocated a fixed radiofrequency power (RF) corresponding to the output power of the amplifier connected to the beam, and a fixed frequency band corresponding to a colour of the frequency reuse scheme. In a multibeam system with reuse of frequencies, the bandwidth allocated to the mission, typically the Ka band from 17.3 GHz to 20.2 GHz, is split up into sub-bands of frequencies or colours. A colour is allocated to each spot of the coverage according to a scheme which makes it possible to minimize the inter-beam interference. For example, in a system operating in the Ka band (20/30 GHz) according to a frequency reuse scheme with four colours and two polarizations, to each spot of the coverage is allocated in a fixed manner a frequency band of 1.4 GHz of bandwidth and an RF power transmitted by a travelling-wave amplifier of some hundred watts. In order to minimize the antenna's inter-beam interference, it is customary to generate identical beams in terms of radiation pattern, leading to spots of equal size throughout the coverage.
Very high throughput satellite systems with fixed allocation of resources have a first drawback in the case of a non-regular geographical distribution of data traffic. Thus in the spots with light data traffic, such as for example rural zones with low user density, part of the frequency and power resources allocated to these spots is not used to serve the light data traffic. Being unable to be allocated to another spot, these resources are wasted. In the spots with heavy data traffic demand, such as for example urban zones with a very high density of users, the frequency and power resources allocated to these spots are not sufficient to serve the data traffic required. Being unable to use the resources allocated to another spot, part of the data traffic will not be served.
Very high throughput satellite systems with fixed allocation of resources have a second drawback in the case of a temporal variation of the data traffic in a spot. This variation may be daily (peak periods), seasonal or during the lifetime of the satellite. Thus at certain moments the data traffic demand is low, part of the allocated frequency and power resources is not used to serve the light data traffic. At other moments, the data traffic demand is very high and the frequency and power resources allocated are not sufficient to serve the peak data traffic.
Thus, very high throughput satellite systems with fixed allocation of resources are not suitable for serving data traffic profiles that vary in space (geographical distribution) and over time (seasonal or daily variations).
Very high throughput satellite systems with fixed allocation of resources have a third drawback. The radiofrequency links in the ka band (20/30 GHz) between the satellite and the user terminals are very sensitive to the phenomena of attenuation and fading of the radio signals due in particular to bad weather (rain, snow, hail, etc.). To maintain the links in case of bad weather, it is customary in very high throughput satellite systems to reduce the data throughput of the disturbed links. This technique is implemented by the introduction of adaptive modulation and adaptive coding or ACM for “Adaptive Coding and Modulation”. Consequently, the data traffic in a spot undergoing bad weather is reduced; it is not possible in these very high throughput satellite systems with fixed resource allocation, to allocate to the spots affected by bad weather more resources in terms of frequency and power in order to counter the attenuations and fadings.
This misfit between the resources in terms of frequency and power and the data traffic variations penalizes the profitability of these very high throughput satellite systems.
An exemplary method, described in American patent U.S. Pat. No. 8,634,296, of frequency allocation for multibeam satellite systems is in particular known. This method takes no account of the phenomena of attenuation of the signal in each spot of the coverage zone or of the interference between adjacent beams and channels.
The invention proposes a method of dynamically allocating the radio resources of a satellite and a very high throughput satellite system configured to implement this method. The method of allocation is executed by a piece of ground equipment called a Radio Resource Manager or RRM. The method of allocation according to the invention, allocates frequency resources dynamically over time to each spot of the multibeam coverage in accord with the conditions of propagation of the radio signals (in particular the attenuations due to bad weather) prevailing in the spots, with the current and future spot data traffic profile, with the level of interferences generated in the neighbouring beams. The method applies preferentially in respect of downgoing forward links, that is to say from the satellite to the user terminals.
In contradistinction to the very high throughput satellite systems according to the prior art in which the frequency plan or frequency reuse scheme typically comprises at most four colours, the frequency plan or the frequency reuse scheme of the method according to the invention comprises tens of colours. For example, the frequency plan of a very high throughput satellite system according to the invention, operating in the Ka band (17.7 GHz to 20.2 GHz), comprises 80 colours of 30 MHz of bandwidth in each polarization. In each polarization, the colours are numbered from 1 to 80. Each spot can be allocated from zero (no traffic in the spot) to 80 frequency sub-bands or colours (maximum traffic in the spot).
A resources allocation configuration is, for each spot of the coverage, the total number and the index numbers of colours allocated to this spot and the radio power allocated to this spot.
The time is split up into time intervals of fixed duration called time slice or slot. To each time slot there corresponds a different resources allocation configuration. During each time slot, the Radio Resource Manager establishes the resources allocation configuration of the next time slot. The resources allocation configuration is established by the method of dynamically allocating radio resources according to the invention.